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    Subject[tip:x86/uv] x86, UV: Fix smp_processor_id() use in a preemptable region
    Commit-ID:  00b30cf04a775b5292ab704f782394e36e25617d
    Gitweb: http://git.kernel.org/tip/00b30cf04a775b5292ab704f782394e36e25617d
    Author: cpw@sgi.com <cpw@sgi.com>
    AuthorDate: Tue, 21 Jun 2011 07:21:26 -0500
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Tue, 21 Jun 2011 14:50:31 +0200

    x86, UV: Fix smp_processor_id() use in a preemptable region

    Fix a call by tunables_write() to smp_processor_id() within a
    preemptable region.

    Call get_cpu()/put_cpu() around the region where the returned
    cpu number is actually used, which makes it non-preemptable.

    A DEBUG_PREEMPT warning is prevented.

    UV does not support cpu hotplug yet, but this is a step toward
    that ability as well.

    Signed-off-by: Cliff Wickman <cpw@sgi.com>
    Link: http://lkml.kernel.org/r/20110621122242.086384966@sgi.com
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    arch/x86/platform/uv/tlb_uv.c | 5 +++--
    1 files changed, 3 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/platform/uv/tlb_uv.c b/arch/x86/platform/uv/tlb_uv.c
    index 68e467f..34be650 100644
    --- a/arch/x86/platform/uv/tlb_uv.c
    +++ b/arch/x86/platform/uv/tlb_uv.c
    @@ -1334,9 +1334,10 @@ static ssize_t tunables_write(struct file *file, const char __user *user,

    instr[count] = '\0';

    - bcp = &per_cpu(bau_control, smp_processor_id());
    -
    + cpu = get_cpu();
    + bcp = &per_cpu(bau_control, cpu);
    ret = parse_tunables_write(bcp, instr, count);
    + put_cpu();
    if (ret)
    return ret;


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